Whitaker was better than Kent. Kent hit a liitle better, but Whitaker's superior fielding more than made up for it.
Sandberg was better, but Whitaker lasted longer.
Grich was slighly better for a short period, but Whitaker had more good years. Grich missed more time to injuries.
Utley was better, but Whitaker had more good years.
I'd put them all in expect maybe Kent. I've always had Kent on the bubble.
You talk about the end of Whitaker's career like it was nothing. He hit a lot better than most platoon players and it wasn't a strict platoon. He accumulated enough plate appearances to get 4.7, 4.1, 2.5, 1.5 WAR from age 35 to 38. Lots of great hitters can't do what he did in the end. He also could still handle middle infield capably up until age 37 which is rare. His consistency and endurance was pretty special and I'm not just saying that as a fan boy.